Linear regression is a means of fitting a line of best
fit to a series of data points. The method is quite
precise, and uses the 'least sums of squares method'. The
output of a linear regression will also provide the
equation of the line (of best fit) in the form of y = mx
+ c. So for any given x value (your independent variable)
you can predict the y value (dependent variable).
There are a variety of ways to do it in Excel.
1) Plot data on a chart, right-click and select <Add
Trendline> and then select linear trendline and checkmark
<Display Equation On Chart>. Here you get the regression
equation.
2) <Tools> <Data Analysis...><Regression>. Follow the
wizard to get a statistical output from which you can
derive the regression equation
3) Use functions like SLOPE, LINEST, INTERCEPT to derive
the regression equation. Look in Excel Help for more on
those.
You may benefit from reading about linear regression. Any
standard statistics book will have a chapter on it and,
realistically, it is relatively painless to get to grips
with the methodology of it all. Interpreting results is
more tricky...
Alex
